Ion-exchanged Channel Waveguides Research Articles

Numerical modeling of field-assisted Ag+–Na+ ion-exchanged channel waveguides using varied explicit space charge density approach

Numerical modeling of field-assisted Ag+–Na+ ion-exchanged channel waveguides using varied explicit space charge density approach

Polarization Conversion by Transformation of the TM0–TE1 Modes in an Ion-Exchange Glass Waveguide

The mode structure of a four-layer optical waveguide consisting of an ion-exchanged channel waveguide in glass coated with a highly refractive nanoscale dielectric film has been studied. It has been found that varying the geometric dimensions of the film changes the polarization states of the second and third waveguide modes: the TM0 mode is transformed into the TE1 mode, and the TE1 mode becomes the TM0 mode. Based on this, a new method of designing a waveguide polarization converter has been proposed and experimentally confirmed.

Nd^3+-doped ion-exchanged aluminum germanate glass channel waveguide

K+–Na+ ion-exchanged channel waveguide has been fabricated in Nd3+ doped aluminum germanate (NMAG) glasses with potential photosensitive property. The channel waveguide exhibits single mode at 1.3μm and the mode field diameters were measured to be horizontally 10.1μm and vertically 5.3μm, respectively. Amplified spontaneous emissions (ASE) of 905, 1060, 1334 and 1816nm originating from the 4F3/2 level were recorded under ~800nm diode laser pumping and the maximum stimulated emission cross-sections for the 4F3/2→4I11/2 and 4F3/2→4I13/2 transitions are derived to be 21.5 × 10−21 and 7.6 × 10−21cm2, respectively. In addition, with 71.8% quantum efficiency and the largest emission intensity among various Nd3+ doping cases, 2wt% Nd2O3 is considered as the optimized doping concentration for the compact channel waveguide. The ion-exchanged Nd3+-doped NMAG glass channel waveguides offer favorable prospects for the development of optical waveguide amplifiers, broadband light sources and infrared UV-written grating waveguide lasers.

White upconversion luminescence in Tm3+/Ho3+/Yb3+ triply doped K+–Na+ ion-exchanged aluminum germanate glass channel waveguide

Rare-earth ions doped K+–Na+ ion-exchanged aluminum germanate (NMAG) glass channel waveguides have been designed and fabricated. Under 980nm laser pumping, an intense upconversion white light transmission trace was observed in Tm3+/Ho3+/Yb3+ triply doped NMAG glass channel waveguide and a high-brightness light spot was achieved from the output end of the fiber connected to the waveguide channel. The fluorescent colors were diverse and located within or near the white region in CIE chromaticity diagram under various pumping powers. These admirable results indicate that Tm3+/Ho3+/Yb3+ triply doped NMAG channel waveguide is a promising light source for medical and high-precision processing illumination.

Numerical and experimental investigation on Ag+–Na+ field assisted ion-exchanged channel waveguides

The characteristics of Ag+ diffusion during field assisted fabrication of a channel waveguide in glass substrates are analyzed using a numerical model. Differences between the results of the author's original model and the other typically used models are discussed. Experimental conditions have been chosen to clearly demonstrate the essential features of Ag+ concentration contours, particularly near the mask edges. Metallic and dielectric masks have been used in the experiment, and the results are similar for both mask materials. The shapes of Ag+ concentration contours reveal the presence of a thin polarized layer under the mask and seem to be consistent with the results predicted by the proposed numerical model. Some modifications of the model are suggested for a better fit of the numerical to the experimental results.

All-Optical and Thermal Tuning of a Bragg Grating Based on Photosensitive Composite Structures Containing Liquid Crystals

We report on the fabrication and characterization of a tunable filtering effect, observed in a waveguide grating made of alternated strips of photocurable polymer and a mixture of azo-dye doped liquid crystal. The grating is sandwiched between two borosilicate glasses, one of which includes an ion-exchanged channel waveguide, which confines the optical signal to be filtered. We analyze the effects of a low power visible, pump light beam that hits the sample and temperature effects. Both effects are investigated experimentally. The application of the pump light allowing the filtered wavelength to be tuned over a 6.6 nm range, while a temperature variation of 4°C, implies a tuning of 14 nm.

Observation of tunable optical filtering in photosensitive composite structures containing liquid crystals

We report on the investigation and characterization of an optically tunable filtering effect, observed in a waveguide grating made of alternated strips of photocurable polymer and a mixture of azo-dye-doped liquid crystal. The grating is sandwiched between two borosilicate glasses, one of which includes an ion-exchanged channel waveguide, which confines the optical signal to be filtered. Exposure to a low power visible light beam modifies the azo-dye molecular configuration, thus allowing the filtered wavelength to be tuned over a 6.6 nm range. Simulations of the filtering response are well described with our experimental findings.

Numerical modeling of field-assisted ion-exchanged channel waveguides by the explicit consideration of space-charge buildup

A numerical model explicitly considering the space-charge density evolved both under the mask and in the region of optical structure formation was used to predict the profiles of Ag concentration during field-assisted Ag(+)-Na(+) ion exchange channel waveguide fabrication. The influence of the unequal values of diffusion constants and mobilities of incoming and outgoing ions, the value of a correlation factor (Haven ratio), and particularly space-charge density induced during the ion exchange, on the resulting profiles of Ag concentration was analyzed and discussed. It was shown that the incorporation into the numerical model of a small quantity of highly mobile ions other than exclusively Ag(+) and Na(+) may considerably affect the range and shape of calculated Ag profiles in the multicomponent glass. The Poisson equation was used to predict the electric field spread evolution in the glass substrate. The results of the numerical analysis were verified by the experimental data of Ag concentration in a channel waveguide fabricated using a field-assisted process.

Radiative Transition Properties of Tm<sup>3+</sup> in Aluminum Germanate Glass for FWW Waveguide Amplifier

Dominant 794nm wavelength upconversion emission, which originates from the Tm3+: 3H4®3H6 transition, has been recorded in Tm3+/Yb3+ codoped aluminum germanate glass under the 974nm wavelength laser excitation. Judd-Ofelt parameters W2 (6.52´10-20cm2), W4 (9.83´10-21cm2) and W6 (1.02´10-20cm2) indicate a higher inversion asymmetric and stronger covalent environment in the glass material. The spontaneous transition probability of 3H4®3H6 was derived to be 1121s-1, which is responsable for obtaining the powerful 794nm emission. K+-Na+ ion-exchanged multimode channel waveguide amplifiers have been fabricated based on the Tm3+/Yb3+ codoped aluminum germanate glass substrate. The relative gain coefficient of a 2.20cm channel waveguide was determined to be 1.58dB/cm at a signal wavelength of 810 nm under 457mW 980nm laser diode excitation.

K + − Na + ion-exchanged sodium magnesium aluminum germanate glass waveguide amplifier operating in the first telecommunications window

Potassium-sodium (K+−Na+) ion-exchanged multimode channel waveguide amplifiers have been fabricated based on Tm3+/Yb3+ codoped sodium magnesium aluminum germanate (NMAG) glass substrates. The normalized optical and relative gain coefficients of a 2.20 cm long device were identified to be 3.65 dB/cm and 1.58 dB/cm, respectively, at a signal wavelength of 810 nm under 457 mW 980 nm laser diode excitation. These are the highest values reported, and the results indicate that Tm3+/Yb3+ codoped NMAG glasses are an attractive material for optical amplification in the first telecommunications window.

Proposal for a simple integrated optical ion-exchange waveguide polarizer with a liquid crystal overlay

A simple, compact electro-optic polarizer based on an ion-exchanged glass channel waveguide covered with a nematic liquid crystal (LC) is proposed. A full-vectorial beam propagation method is employed to simulate this device for the first time. For the cases of zero and strong LC surface anchoring, the performance of the proposed polarizer under different applied voltages is analyzed numerically. Analysis indicates that surface anchoring of the liquid crystal is a key issue influencing the performance for the proposed optical polarizer device.

Extraction of phase derivative data from interferometer images using a continuous wavelet transform to determine two-dimensional refractive index profiles

Two-dimensional refractive index profiles of ion exchanged channel waveguides in glass have been obtained from the analysis of interferometer data. To obtain depth data, a shallow bevel is produced in the glass by polishing. The refractive index profile information that is contained within the derivative of the phase data is extracted directly using a continuous wavelet transform algorithm. The algorithm used to characterize and smooth the wavelet ridge is discussed in detail.

Radiation and gain behaviors in Tm^3+-doped aluminum germanate substrate glasses and thermal ion-exchanged waveguide

Tm3+ -doped acid-resistant aluminum germanate (NMAG) glasses and a K+–Na+ ion-exchanged channel waveguide have been fabricated and characterized. Judd–Ofelt intensity parameters indicate a high asymmetry and strong covalent environment in NMAG glasses. A remarkable internal gain coefficient of 0.48 dB∕cm at 1.482 μm wavelength was achieved in the 3.15 cm long channel waveguide. Based on absorption and emission cross-sections, the ideal internal gain coefficient at 1.675 μm and 1.815 μm is given to be 0.5 dB∕cm and 2.0 dB∕cm, respectively, as the population inversion equals 1.0. Experimental results and theoretical anticipation indicate that Tm3+ -doped NMAG glasses are potential and attractive substrates in developing S- and U-band waveguide amplifiers and an eye-safe medical laser.

Measurement of two dimensional refractive index profiles of channel waveguides using an interferometric technique

Two dimensional refractive index profiles of ion exchanged channel waveguides in glass have been measured using an interferometric method. In order to obtain depth data, a shallow bevel is produced in the glass by polishing. A regularization algorithm for the extraction of the phase data from the interferometer image is presented. The method is applied to waveguides formed by the electric field assisted diffusion of Cu+ ions into a borosilicate glass. The index change obtained from the interferometer is in good agreement with that obtained from measurements on planar waveguides.

Tm 3 + -doped ion-exchanged aluminum germanate glass waveguide for S-band amplification

K + – Na + ion-exchanged channel waveguide amplifiers have been fabricated in Tm3+-doped acid-resistant aluminum germanate glasses. The optical and relative gains of a 3.15-cm-long waveguide channel were achieved to be 4.05 and 2.29 dB at 1.482 μm wavelength under 110 mW 793 nm laser excitation, respectively. After compensating the propagation loss, an internal gain of 1.50 dB and a remarkable gain coefficient of 0.48 dB/cm were obtained, which reveals a definite S-band signal amplification in the low phonon energy glass waveguide. As an expectation, UV-radiation-sensitive glass waveguide should promote the developments of gain-flatten S-band waveguide amplifiers, infrared UV-writing grating waveguide lasers, and compact multifunctional integrated optical devices.

Radiative transitions and optical gains in Er^3+/Yb^3+ codoped acid-resistant ion exchanged germanate glass channel waveguides

K+-Na+ ion-exchanged channel waveguide amplifiers have been fabricated in Er3+/Yb3+ codoped acid-resistant aluminum germanate (NMAG) glasses. The Judd-Ofelt parameters indicate high asymmetry and strong covalent environment in the glass substrates. The optical gain and the relative gain (the signal enhancement) of a 2.5 cm long waveguide amplifier were measured to be 9.10 and 8.16 dB, respectively, and after compensating both the propagation loss and the absorption loss, a maximum internal gain of ~2.0 dB at 1.534 μm was obtained, which reveals the successful employment of the thermal ion-exchange technology on the low phonon energy glasses. Based on this work, ion-exchanged Pr3+, Tm3+, and Ho3+ doped NMAG glass waveguides will bring surprises in developing O-, S- and U-band waveguide amplifiers, infrared UV-writing grating waveguide lasers, and compact integrated optical devices.

Tunable integrated optical filter made of a glass ion-exchanged waveguide and an electro-optic composite holographic grating

We report the fabrication and the optical characterization of a hybrid tunable integrated optical filter. It consists of a diffused ion-exchanged channel waveguide on a borosilicate glass substrate with a cover of the same glass to form a gap filled with a holographic grating. The grating morphology, called POLICRYPS (POlymer LIquid CRYstal Polymer Slices), is made of alternating stripes of polymer and liquid crystal acting as overlayer for the underneath waveguide. The filter structure includes aluminum coplanar electrodes to electrically control the grating properties, allowing the tunability of the filter. The electric driving power required to tune the filter obtained was in the range of submilliwatts due to the efficient liquid crystal electro-optic effect.

Low-loss channel waveguides and Y-splitter formed by ion-exchange in silica-on-silicon

Low-loss ion-exchanged sol-gel channel waveguides on silicon substrate were fabricated. Ion-exchangeable aluminosilicate glass film was fabricated by sol-gel technique. Ag(+)-Li(+) thermal ion-exchange was used to achieve single mode channel waveguide. Propagation loss of 0.50 dB/cm and coupling loss of 0.76 dB/facet were measured by cutback method. A Y-branch power splitter was also fabricated. The results demonstrate that ion-exchange technique can be applied to prepare low-loss channel waveguides in thin film structures.

Highly sensitive spectroscopic detection of heme-protein submonolayer films by channel integrated optical waveguide

A highly sensitive technique based on optical absorption using a single-mode, channel integrated optical waveguide is described for broad spectral band detection and analysis of heme-containing protein films at a glass/water interface. Fabrication steps and device characteristics of optical waveguides suitable for operation in the wavelength range of 400 - 650 nm are described. Experimental results reported here show a limit of detection smaller than 100 pg/cm(2) for a submonolayer of ferricytochrome c by probing the Soret transition band with a 406-nm semiconductor diode laser propagating in a single-mode, ion-exchanged channel waveguide. By taking advantage of the exceptionally low limit of detection, we examined the adsorption isotherm of cytochrome c on a glass surface with unprecedented detail. Unlike other surface-specific techniques (e.g. SPR, integrated optic Mach-Zehnder interferometer) that probe local refractive-index changes and therefore are very susceptible to temperature fluctuations, the integrated optical waveguide absorption technique probes molecular-specific transition bands and is expected to be less vulnerable to environmental perturbations.

Photosensitivity and volume gratings in phosphate glasses for rare-earth-doped ion-exchanged optical waveguide lasers

Phosphate glasses containing enough sodium to allow the fabrication of optical channel waveguides by ion exchange are photosensitive to intense ultraviolet irradiation from excimer lasers at 193 and 248nm. Permanent submicrometer-period volume index gratings with modulation amplitudes larger than 10−4 were obtained even after annealing the irradiated samples for 2h at 230°C. Ultraviolet-visible absorption changes were measured in the irradiated areas, as well as structural modifications observed by surface profiling. Comparative studies were carried out for glasses that were also codoped with erbium and ytterbium to provide high gain at wavelengths near 1.5μm. Finally, we demonstrate narrowband gratings with reflectivities larger than 80% in silver ion-exchanged channel waveguides made in these phosphate glass substrates.